Method for preparing steam or hot water by using waste heat of cooling water

Abstract

The present invention provides a method for preparing steam or hot water and a system for implementing the same, the method comprising: (S1) introducing a process waste heat fluid supplied from a plurality of waste heat sources into each of a plurality of heat exchangers arranged in a number corresponding to the plurality of waste heat sources to exchange heat with cooling water; (S2) introducing cooling water heated by heat exchange with the process waste heat fluid in each heat exchanger into a refrigerant evaporator via an integrated pipe, and then heat-exchanging with the refrigerant to evaporate the refrigerant; (S3) compressing the vaporized refrigerant flow in a refrigerant compressor; (S4) subjecting the compressed refrigerant stream to heat exchange with water in the refrigerant condenser, thereby condensing the refrigerant stream and obtaining steam or hot water; and (S5) flowing the condensed refrigerant flow through a refrigerant expansion valve for pressure reduction and then circulating into the refrigerant evaporator.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of priority to Korean Patent Application Nos. 10-2023-0050549 and 10-2024-0021815, filed on April 18, 2023 and February 15, 2024, respectively, which are incorporated herein by reference in their entirety. Technical Field

[0003] The present invention relates to a method for producing steam or hot water by utilizing waste heat of cooling water, and more specifically, to a method for producing steam or hot water by recovering waste heat of cooling water heated after heat exchange between multiple waste heat sources generated in a petrochemical process and cooling water. Background Art

[0004] Petrochemical processes use large amounts of energy to produce products, and the energy used is either discarded or reused.

[0005] Steam used as an energy source in petrochemical processes is usually produced using boilers by the heat of combustion of hydrocarbon fuels (see Figure 1 ), but the process involves high costs and discharges the supplied fuel into the atmosphere in the form of carbon dioxide through combustion, causing global warming.

[0006] Therefore, in order to reduce carbon emissions and lower manufacturing costs of petrochemical products, methods for reducing steam use in processes, methods for using waste heat, etc. have emerged.

[0007] Generally, petrochemical products can be manufactured through processes including reaction, separation, purification, etc. When steam is used to heat the lower part of a column where these processes are performed, a high-temperature process fluid is produced in the upper part of the column.

[0008] Reference Figure 2 , the high temperature fluid prepared in the petrochemical process can be a waste heat (WH) source, and is cooled by heat exchange with cooling water in a heat exchanger (HE) (such as a condenser or a cooler) to lose a large amount of heat, and the heated cooling water is introduced into a cooling tower (CT), cooled while dissipating heat, and then supplied back to the heat exchanger. The heat dissipated in this cooling process can be called waste heat within the process.

[0009] Since the cooling tower forcibly dissipates heat by bringing the cooling water into contact with the atmospheric air, the heat rejected from the cooling tower cannot be recovered, resulting in very large heat losses.

[0010] Therefore, there is a need for a method for effectively recovering waste heat from cooling water heated by heat exchange with a high-temperature fluid (waste heat source) prepared in various processes (such as reaction, separation and purification) during the manufacture of petrochemical products, and reusing the recovered waste heat. Summary of the invention

[0011] Technical issues

[0012] The present invention aims to solve the problems mentioned in the background technology and provides a method for recovering waste heat in the following manner: cooling water is heated after heat exchange between multiple waste heat sources generated in a petrochemical process and each of them is subjected to heat exchange. The method introduces the cooling water into a heat pump device and utilizes the recovered waste heat to prepare a large amount of steam or hot water required for the process.

[0013] Technical Solution

[0014] According to one embodiment of the present invention, a method for preparing steam or hot water is provided, which comprises: (S1) introducing a process waste heat fluid supplied from a plurality of waste heat sources into each of a plurality of heat exchangers configured in a number corresponding to the plurality of waste heat sources to exchange heat with cooling water; (S2) introducing the cooling water heated by heat exchange with the process waste heat fluid in each heat exchanger into a refrigerant evaporator via an integrated pipe, and then exchanging heat with the refrigerant to evaporate the refrigerant; (S3) compressing the evaporated refrigerant flow in a refrigerant compressor; (S4) exchanging heat between the compressed refrigerant flow and water in a refrigerant condenser, thereby condensing the refrigerant flow and obtaining steam or hot water; and (S5) passing the condensed refrigerant flow through a refrigerant expansion valve for reducing pressure, and then circulating it to the refrigerant evaporator.

[0015] The linear length of the manifold may be from 5m to 5,000m and may be controlled to maintain a flow rate of from 0.5m / s to 5m / s.

[0016] The temperature of the compressed refrigerant stream may be 90°C to 200°C, and the temperature of the refrigerant stream condensed by heat exchange with water in the refrigerant condenser may be 85°C to 170°C.

[0017] The vapor obtained in the refrigerant condenser may be transferred to a vapor compressor to be further compressed and converted into high-pressure vapor.

[0018] According to another embodiment of the present invention, a system for preparing steam or hot water is provided, which includes: multiple waste heat sources, heat exchangers configured in a number corresponding to the multiple waste heat sources, and a heat pump device connected to the heat exchanger through an integrated pipe and a branch pipe, wherein the heat pump device includes a refrigerant evaporator, a refrigerant compressor, a refrigerant condenser and a refrigerant expansion valve connected by pipes, and the heated cooling water flowing out of each heat exchanger is collected through the integrated pipe and introduced into the refrigerant evaporator of the heat pump device, and then heat-exchanges with the refrigerant to evaporate the refrigerant, and then passes through the branch pipe and then circulates to each heat exchanger.

[0019] The system may comprise a further vapour compressor connected to the refrigerant condenser of the heat pump device.

[0020] Beneficial Effects

[0021] According to the present invention, a plurality of waste heat sources each perform heat exchange with cooling water, and each heated cooling water is introduced into a heat pump device through an integrated pipe to perform heat exchange with a refrigerant circulating in the heat pump device, thereby recovering waste heat of the heated cooling water. The waste heat of the cooling water is used to evaporate the refrigerant, which is compressed using electricity and exchanges heat with water, thereby obtaining a large amount of steam or hot water required in the process.

[0022] In addition, when the waste heat of the cooling water recovered in the heat pump device is used to obtain steam, the compressed refrigerant and the condensed refrigerant are each controlled to show a temperature that maximizes the temperature rise, and the steam is subjected to additional compression to be converted into a final compressed steam of high temperature and high pressure, which is then used as an energy source in various process steps. This can reduce the manufacturing cost of petrochemical products and reduce carbon emissions.

[0023] In addition, since the present invention is applicable to multiple waste heat sources generated in various petrochemical processes, it is possible to recover waste heat from multiple (e.g., 10 to 100) cooling water heat exchangers in a petrochemical plant, and waste heat recovery can be achieved in a single heat pump device through an integrated pipe. In particular, by controlling the flow rate of the integrated pipe within a predetermined range to maintain a uniform mixing state of the heated cooling water, cost reduction, maintenance minimization, stable operation, etc. can be achieved through simplification of steam preparation equipment and operation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a diagram schematically showing a steam generation process using a boiler.

[0025] Figure 2 is a diagram schematically showing a process of exchanging heat between a waste heat source prepared in various petrochemical processes and cooling water and then cooling the heated cooling water in a cooling tower.

[0026] Figure 3 is a diagram showing a process of performing heat exchange between each of a plurality of waste heat sources and cooling water and then cooling the heated cooling water in a heat pump device to recover waste heat and prepare steam or hot water required in a process according to the present invention.

[0027] Figure 4 is a diagram showing a process of obtaining high-pressure steam by additionally connecting a steam compressor to a refrigerant condenser of a heat pump device according to the present invention.

[0028] Figure 5 is a diagram showing a process of exchanging heat between each of a plurality of waste heat sources and cooling water and then cooling the heated cooling water in a cooling tower in a comparative example. DETAILED DESCRIPTION

[0029] The terms and words used in this specification and claims should not be interpreted as general or dictionary meanings, but should be interpreted as meanings and concepts that satisfy the technical ideas of the present invention based on the principle that inventors can appropriately define the concepts of the terms in order to describe their own inventions in the best mode.

[0030] The terms “include” or “comprising” used herein specifically indicate specific properties, regions, integers, steps, operations, elements or components, and do not exclude the existence or addition of other specific properties, regions, integers, steps, operations, elements, components or groups thereof.

[0031] The term "flow" used herein may refer to a fluid flow in a process, and may also refer to the fluid itself flowing in a pipe. Specifically, flow may refer to the fluid itself and the flow of the fluid flowing in the pipe connecting each device. In addition, the fluid may include any at least one component of a gas, a liquid, and a solid.

[0032] One embodiment of the present invention relates to a method for preparing steam or hot water by heat exchange between multiple waste heat sources and cooling water and then recovering the waste heat of the heated cooling water. Specifically, the method includes the following steps: (s1) performing heat exchange between multiple process waste heat fluids and cooling water, (s2) integrating the cooling water heated by the heat exchange and then performing heat exchange with a refrigerant to evaporate the refrigerant, (s3) compressing the evaporated refrigerant flow, (s4) performing heat exchange between the compressed refrigerant flow and water to condense the refrigerant flow and obtain steam or hot water, and (S5) decompressing the condensed refrigerant flow.

[0033] The method for preparing steam or hot water is described in detail below with reference to the accompanying drawings.

[0034] Reference Figure 3According to the method for preparing steam or hot water by recovering waste heat of cooling water according to the present invention, a system for preparing steam or hot water can be performed, which includes a plurality of waste heat sources 100, heat exchangers 200 configured in a number corresponding to the plurality of waste heat sources, and a heat pump device 300 connected to the heat exchanger through an integrated pipe and a branch pipe.

[0035] The plurality of waste heat sources 100 may include high temperature process waste heat fluids generated in various processes such as reaction, separation and purification when manufacturing petrochemical products. The temperature of the high temperature process waste heat fluid may vary according to the conditions of each process. For example, it may be approximately in the range of 20°C to 250°C, specifically 30°C to 150°C.

[0036] If this process waste heat fluid is wasted without separate heat recovery, it is undesirable from an energy perspective. Therefore, it is necessary to recover heat from the waste heat source 100, i.e., from the high temperature process waste heat fluid, and use the recovered heat in other processes that require heat, reducing energy use in the entire process.

[0037] To this end, the process waste heat fluid (WH1, WH2, WH3, ...) can be supplied to the heat exchanger (HE1, HE2, HE3, ...) using cooling water. The process waste heat fluid can exchange heat with the cooling water in the heat exchanger (HE1, HE2, HE3, ...) so that the heat of the process waste heat fluid can be transferred to the cooling water. In addition, the cooling water whose temperature has been increased by the received heat can be supplied to the refrigerant evaporator described later and used as a heat source for evaporating the refrigerant.

[0038] Specifically, since the process waste heat fluids (WH1, WH2, WH3, . . . ) may each have different fluid properties, such as composition and temperature, it may be inappropriate to directly supply the process waste heat fluids to the refrigerant evaporator. For the operational stability and reliability of the refrigerant evaporator, the process waste heat fluids are each first heat-exchanged with cooling water in a heat exchanger (sometimes referred to as a cooling water heat exchanger), and then, preferably, the high-temperature cooling water is supplied from the heat exchanger to the refrigerant evaporator.

[0039] In one embodiment of the present invention, the heat exchanger 200 is connected to a plurality of waste heat sources 100 and can be configured in a number (HE1, HE2, HE3, ...) corresponding to the process waste heat fluid (WH1, WH2, WH3, ...). In such a heat exchanger, cooling water circulates to cool or condense the waste heat source 100.

[0040] Typically, in a petrochemical plant, a plurality of cooling water heat exchangers, such as about 10 to 100 cooling water heat exchangers, are operated to cool or condense high temperature process fluids prepared in various processes. The present invention utilizes a plurality of cooling water heat exchangers simultaneously. To this end, the cooling water heat exchangers can each be individually connected to a plurality of waste heat sources to cool or condense the high temperature process fluids and recover heat therefrom, while the cooling water circulating in each heat exchanger is heated by the recovered heat, and then the heated cooling water can be supplied to a refrigerant evaporator, thereby simultaneously processing a large amount of process waste heat fluids.

[0041] The heat exchanger may include a cooler or condenser commonly used in petrochemical processes. In order to improve heat exchange efficiency, the heat exchanger suitable for the present invention may be a common shell and tube type, or a plate type or a falling film evaporator type, but is not limited thereto.

[0042] In one embodiment of the present invention, cooling water at 10°C to 50°C, specifically 20°C to 40°C, can be supplied to each heat exchanger (HE1, HE2, HE3, . . . ) and circulated under a pressure of 1 bar to 10 bar, specifically a pressure of 2 bar to 10 bar and a flow rate of 10 tons / hour to 1,000,0000 tons / hour, specifically 20 tons / hour to 100,000 tons / hour.

[0043] Specifically, when high-temperature (e.g., 20° C. to 250° C.) process waste heat fluid (WH1, WH2, WH3, ...) supplied from a plurality of waste heat sources 100 is introduced into each heat exchanger (HE1, HE2, HE3, ...) in which cooling water circulates, the cooling water can absorb heat from the process waste heat fluid and raise its temperature through mutual heat exchange. In this case, it is advantageous to adjust the temperature raising range of the cooling water to 13° C. to 60° C., for example, 15° C. to 50° C., so as to maintain the temperature difference with the process waste heat within an appropriate range.

[0044] Meanwhile, the flow rate of the process waste heat fluid introduced into each heat exchanger (HE1, HE2, HE3, ...) is not particularly limited, but may be, for example, 0.1 ton / hour to 100,000 ton / hour, specifically 0.5 ton / hour to 50,000 ton / hour or 1 ton / hour to 40,000 ton / hour. The process waste heat fluid heat-exchanged with the cooling water in each heat exchanger (HE1, HE2, HE3, ...) may flow out of each heat exchanger at a temperature lower than the initial temperature (e.g., in the range of 15°C to 200°C).

[0045] Thereafter, after supplying heat to the refrigerant evaporator, the cooling water heated in each heat exchanger (HE1, HE2, HE3, . . . ) is cooled, and then needs to be circulated to the heat exchanger (cooling water heat exchanger) in order to cool or condense the high-temperature process waste heat fluid in the process (i.e., recover the heat of the process waste heat fluid).

[0046] In the present invention, the cooling water heated in each heat exchanger (HE1, HE2, HE3, . . . ) is merged in an integrated pipe 10, and then the cooling water flow merged in the integrated pipe 10 can be supplied to the heat pump device 300, specifically, to the refrigerant evaporator (EV).

[0047] If each cooling water flow is directly supplied to the refrigerant evaporator (EV) provided in the heat pump device 300, each cooling water flow heated in each heat exchanger (HE1, HE2, HE3, ...) may be inconsistent in temperature and flow rate, which may hinder the stable operation of the refrigerant evaporator (EV) and excessively increase the equipment cost for solving such problems of the refrigerant evaporator (EV). In addition, the unstable operation of the refrigerant evaporator (EV) may cause overcooling or insufficient cooling of the refrigerant, which may also hinder the operational stability of other equipment (such as the refrigerant compressor (CP)) provided in the heat pump device 300.

[0048] According to one embodiment of the present invention, the heated cooling water flows are each merged in an integrated pipe 10 and supplied, thereby ensuring the uniformity of the flow rate and temperature of each heated cooling water flow. Specifically, the integrated pipe 10 can be a header type pipe with covers at both ends to collect the heated cooling water flows flowing out of each heat exchanger (HE1, HE2, HE3, ...) configured in parallel. In order to supply the cooling water flow to the refrigerant evaporator (EV) of the heat pump device 300 while maintaining a uniform mixing state, it is necessary to design the length of the integrated pipe and the flow rate of the working fluid to an appropriate range.

[0049] Specifically, the straight length of the integrated pipe 10 can be 5m to 5,000m, specifically 10m to 1,000m. If the length of the integrated pipe is less than 5m, since the heat mixing of the heated cooling water becomes uneven, the refrigerant evaporation rate in the refrigerant evaporator (EV) of the heat pump device 300 changes due to heat exchange, and surge or cavitation may occur in the refrigerant compressor (CP) of the rear section, causing the drive itself to become impossible. If the length of the integrated pipe exceeds 5,000m, heat loss may occur, reducing the amount of waste heat or increasing the pipe pressure difference, resulting in increased power.

[0050] In addition, the flow rate of the integrated pipe 10 may be 0.5 m / s to 5 m / s, specifically 1 m / s to 3 m / s. If the flow rate of the integrated pipe is less than 0.5 m / s, the thermal mixing efficiency of the heated cooling water may be reduced. If the flow rate of the integrated pipe exceeds 5 m / s, corrosion may occur in the pipe.

[0051] By applying the integrated pipe 10 as described above, cost reduction, maintenance minimization, and operation stability can be achieved through simplification and operational efficiency of steam preparation equipment.

[0052] At the same time, if the waste heat of the cooling water is recovered by connecting a heat pump device to each cooling water that exchanges heat with each single waste heat source, multiple heat pump devices for heat exchangers corresponding to multiple waste heat sources may be required, making it difficult to obtain the economic effect of replacing the cooling tower (which is a means of cooling the heated cooling water in conventional methods).

[0053] In the present invention, multiple cooling water flows are heated by heat exchange with multiple waste heat sources, then merged in an integrated pipe, and then supplied to a heat pump device, thereby obtaining advantages compared to operating multiple heat pump devices, such as simplified control and operation, reduced number of abnormal operations, and increased replacement cycle.

[0054] In addition, if the heat pump device is connected to each cooling water that is heat-exchanged with a single waste heat source, there may be waste heat sources that cannot be recovered due to the limitation of small-capacity equipment. However, in the present invention, even trace amounts of waste heat can be recovered by supplying multiple heated cooling water flows to the heat pump device through an integrated pipe.

[0055] In addition, if multiple heat pump devices are operated separately, it may be difficult to control the material balance of the entire facility. However, the present invention can be applied by integrating a single heat pump device through an integrated pipe, thereby controlling a more effective material balance, thereby improving operational stability and reducing maintenance times.

[0056] The heat pump device 300 used in the present invention circulates a low-temperature heat source to a high temperature or a high-temperature heat source to a low temperature through the evaporation or condensation heat of the refrigerant. The components of the refrigerant evaporator (EV), the refrigerant compressor (CP), the refrigerant condenser (CD) and the refrigerant expansion valve (EP valve) are connected by pipes so that the refrigerant can circulate.

[0057] The refrigerant evaporator (EV) is a component that vaporizes and evaporates the refrigerant through heat exchange between a high-temperature fluid and the refrigerant, and in order to improve the heat exchange efficiency, each refrigerant evaporator suitable for the present invention can be a general shell and tube type, and can also be a plate type or falling film evaporator type, but is not limited to this.

[0058] Low temperature and low pressure liquid refrigerant, for example, refrigerant having a pressure of 0.5 bar to 40 bar or 1 bar to 20 bar and a temperature of 10° C. to 60° C. or 15° C. to 50° C., respectively, may be introduced into the refrigerant evaporator (EV). When the heated refrigerant stream flowing out of each heat exchanger (HE1, HE2, HE3, . . . ) and converging in the integrated pipe 10 is introduced into the refrigerant evaporator (EV), the low temperature and low pressure refrigerant flows in the refrigerant evaporator (EV), and the refrigerant is vaporized by heat exchange.

[0059] That is, when the mixed flow of cooling water heated to a range of 13°C to 60°C is introduced into the refrigerant evaporator (EV), the refrigerant absorbs heat through mutual heat exchange and can be converted into an air flow with a relatively high temperature. At the same time, the heated cooling water supplies heat in the refrigerant evaporator, thereby being cooled to a range of 10°C to 50°C, and then circulates to each heat exchanger (HE1, HE2, HE3, . . . ) through a plurality of branch pipes connected to the pipe 20.

[0060] If necessary, a pump for effectively circulating cooling water may be installed at the rear end of the refrigerant evaporator (EV), through which the heated cooling water is introduced and flows.

[0061] In one embodiment of the present invention, the total flow rate of the refrigerant introduced into the refrigerant evaporator (EV) through the integrated pipe 10 can be 10 tons / hour to 1,000 tons / hour, for example, 20 tons / hour to 500 tons / hour or 30 tons / hour to 400 tons / hour, and the flow rate of the mixed flow of heated cooling water introduced into the refrigerant evaporator (EV) can be 0.1 tons / hour to 100,000 tons / hour, for example, 0.5 tons / hour to 50,000 tons / hour or 1 ton / hour to 40,000 tons / hour, but is not limited thereto.

[0062] Next, the refrigerant flow vaporized in the refrigerant evaporator (EV) is introduced into the refrigerant compressor (CP) and compressed by supplying electric energy to increase its pressure. In this case, the temperature of the gaseous refrigerant flow can also be increased in proportion to the amount of electric energy supplied.

[0063] When the refrigerant compressor (CP) is a device capable of compressing a gas stream, various devices known in the art can be used without limitation. For example, a turbo compressor capable of compressing a large capacity can be used. In addition, depending on the capacity of the introduced refrigerant stream, the refrigerant compressor (CP) can be applied alone or in the form of a plurality of refrigerant compressors connected in series.

[0064] The refrigerant compressor (CP) can increase the pressure of the gaseous refrigerant flow introduced through the refrigerant evaporator (EV) by 1.2 to 5 times or 1.4 to 4.5 times. For example, the pressure of the refrigerant flow passing through the compressor CP can be 0.5 bar to 50 bar or 1 bar to 40 bar, and when the compression of the gaseous refrigerant flow is performed within the above range, the type selection, design and manufacture of the compressor are easy to implement.

[0065] In addition, the temperature of the refrigerant stream compressed by the compressor CP can be adjusted to a range of 90° C. to 200° C. or 105° C. to 180° C. When the temperature of the compressed refrigerant stream is less than 90° C., there will be a problem of rapid decrease in heat exchange efficiency with water in the refrigerant condenser of the rear stage, and when the temperature of the compressed refrigerant stream exceeds 200° C., it will cause carbonization of the refrigerant or the compressor lubricating oil, or excessive increase in the refrigerant vapor pressure may make the manufacture of the equipment impossible or cause incomplete operation.

[0066] Thereafter, the high-temperature / high-pressure refrigerant flow flowing out of the compressor is introduced into the refrigerant condenser (CD), and heat exchange can be performed between the high-temperature / high-pressure refrigerant flow compressed in the refrigerant condenser (CD) and water supplied from the outside, thereby condensing the refrigerant flow and obtaining steam or hot water.

[0067] In order to improve the heat exchange efficiency, the refrigerant condenser (CD) applicable to the present invention can be a general shell and tube type, or a plate type or a falling film evaporator type, but is not limited thereto. In addition, according to the capacity of the introduced refrigerant flow, the refrigerant condenser (CD) can be applied alone, or in the form of a plurality of refrigerant condensers connected in series.

[0068] In the refrigerant condenser (CD), when the refrigerant exchanges heat with water to release heat, the refrigerant can be condensed from a high-temperature / high-pressure gas flow into a low-temperature liquid flow, and water supplied from the outside can absorb the heat generated by condensing the refrigerant to be converted into high-temperature hot water or steam.

[0069] More specifically, in the present invention, when a gaseous refrigerant flow (which is obtained by recovering waste heat of cooling water heated in a heat pump device) is compressed by supplying electric power and then the compressed refrigerant flow is circulated to a refrigerant condenser (CD) for heat exchange with water, hot water or steam can be selectively obtained by changing the discharge pressure of water passing through the refrigerant condenser (CD).

[0070] For example, after heat is supplied to water from a refrigerant condenser (CD), when the outlet pressure of the pipe from which the water is discharged is adjusted to be higher than the vapor pressure by a valve, liquid hot water having a temperature of about 85°C to 180°C, specifically 100°C to 150°C, can be prepared by heat exchange between the compressed refrigerant flow and the water. In this case, when the discharge pressure of the water passing through the refrigerant condenser is adjusted based on the vapor pressure, the vapor pressure can be determined according to the temperature of the discharged water. Therefore, when the temperature of the water discharged from the condenser is 90°C, the outlet pressure of the pipe can be set to 0.7 bar or more, when the temperature of the discharged water is 100°C, the output pressure of the pipe can be set to 1 bar or more, and when the temperature of the discharged water is 150°C, the outlet pressure of the pipe can be adjusted to 4.8 bar or more.

[0071] The hot water discharged from the refrigerant condenser (CD) can be used as high-temperature process water in petrochemical processes (for example, boiler feed water or heat source water for emulsion polymerization), and since waste heat and electricity are used in the preparation of this hot water, it is very efficient in terms of energy consumption compared to the existing method of preparing hot water by mixing steam with ordinary industrial water.

[0072] Meanwhile, when the outlet pressure of the pipe discharging water supplied with heat through the refrigerant condenser (CD) is adjusted to be less than the vapor pressure, the hydrogen bonds of the water molecules may be broken due to the heat exchange between the compressed refrigerant flow and the water, thereby preparing gaseous steam. As described above, the vapor pressure as the standard of the output pressure of the pipe can be determined according to the temperature of the discharged water.

[0073] Furthermore, in the above process, hot water and steam may flow out of the refrigerant condenser (CD) in a mixed state.

[0074] In one embodiment of the present invention, the refrigerant stream condensed by heat exchange with water in the refrigerant condenser (CD) is preferably maintained at a saturation temperature of 85° C. to 170° C. at a high pressure of 3 bar to 50 bar or 6 bar to 40 bar. If the temperature of the condensed refrigerant stream is less than 85° C., the pressure of the water in the refrigerant condenser (CD) may be lower than the atmospheric pressure, and thus the steam or hot water prepared by heat exchange may be contaminated and cannot be used for the process. If the temperature of the condensed refrigerant stream exceeds 170° C., carbonization of the refrigerant or compressor lubricating oil may occur, or an excessive increase in the refrigerant vapor pressure may make the manufacture of the equipment impossible or result in incomplete operation.

[0075] Thus, in order to ensure that the temperature of the condensed refrigerant stream is above 85°C, it is advantageous to adjust the critical temperature of the refrigerant to above 100°C. The critical temperature of the refrigerant is a physical property value that is thermodynamically unique to each material, and physically refers to the maximum temperature at which the gas phase and the liquid phase can be distinguished. When this critical temperature differs from the temperature of the condensed refrigerant stream by more than 15°C, the heat exchange potential of the refrigerant can be maintained. If the heat exchange potential in the refrigerant condenser is reduced and the temperature of the condensed refrigerant stream is less than 85°C, the temperature rise for obtaining steam or hot water is insufficient, resulting in malfunction problems such as compressor surge.

[0076] In the present invention, if the refrigerant satisfies the critical temperature condition of the refrigerant as described above, the refrigerant can be selected from various types known in the art without any particular limitation. For example, one or more refrigerants selected from the group consisting of hydrofluorocarbon (HFC) series R245fa, R134a, R1234ze and R1234yf and hydrofluoroolefin (HFO) series R1234ze (E), R1234ze (Z) and R1233zd (E) can be used.

[0077] In addition, the pressure of the condensed refrigerant stream may be maintained at a high pressure of 3 bar to 50 bar or 6 bar to 40 bar, but is not limited thereto.

[0078] Meanwhile, the water supplied to the refrigerant condenser (CD) is preferably pure water in which ions and oxygen are removed, and may be introduced at a temperature of 10° C. to 100° C. or 20° C. to 95° C. and a pressure of 1 bar to 20 bar or 1.5 bar to 10 bar. In addition, the flow rate of the water supplied to the refrigerant condenser (CD) may be 1 ton / hour to 100 tons / hour, for example, 2 tons / hour to 80 tons / hour or 3 tons / hour to 50 tons / hour, but is not limited thereto.

[0079] The steam or a mixed state of steam and hot water prepared by heat exchange with the high temperature / high pressure gaseous refrigerant flow in the refrigerant condenser (CD) may exhibit a temperature of 95 to 200°C or 100 to 180°C and a pressure of 0.5 to 16 bar or 1 to 10 bar.

[0080] Thereafter, the liquid refrigerant flow flowing out of the refrigerant condenser (CD) may be decompressed by passing through a refrigerant expansion valve (EP valve), and the refrigerant flow passing through the refrigerant expansion valve may be circulated to the refrigerant evaporator (EV).

[0081] The refrigerant expansion valve (EP valve) is a device that reduces the pressure and temperature of the refrigerant flow liquefied in the condenser so that the refrigerant flow can be easily evaporated in the evaporator and controls the flow rate of the refrigerant flow. That is, when the liquid refrigerant flow that has passed through the expansion valve enters the refrigerant evaporator again, it will be evaporated even at a relatively low temperature because both the pressure and boiling point are reduced.

[0082] For example, the refrigerant flow through the expansion valve may be in the form of a low temperature / low pressure liquid phase, exhibiting a pressure of 0.5 to 30 bar or 1 to 20 bar and a temperature of 10 to 60° C. or 20 to 50° C., respectively.

[0083] The expansion valve (EP valve) applicable to the present invention can be formed into various structures, such as an electric expansion valve, a thermostatic expansion valve and an automatic expansion valve. In addition, according to the capacity of the introduced refrigerant flow, the expansion valve can be applied one, or in the form of a plurality of expansion valves connected in series.

[0084] Meanwhile, when the steam flowing out of the refrigerant condenser (CD) has a low pressure of 0.5 bar to 16 bar, it may be difficult to directly use the steam in the process, and thus it is preferable to convert the steam into high-pressure steam by performing additional compression.

[0085] like Figure 4 As shown, the steam compressor (S-CP) can be connected to the refrigerant condenser (CD) of the heat pump device 300, and the steam flowing out of the refrigerant condenser (CD) can be introduced into the steam compressor (S-CP) to increase the pressure of the final steam to a range of 2 bar to 60 bar or 3 bar to 30 bar.

[0086] Similar to the above-mentioned refrigerant compressor (CP), the steam compressor (S-CP) may use a turbine type compressor capable of handling a large capacity, may be supplied with electric energy to compress water molecules, and may increase the temperature of steam in proportion to the amount of supplied electric energy.

[0087] In this case, since the heat exchange efficiency of the superheated steam is reduced when input into the heat exchanger in the process, supplementary water may be supplied to prepare saturated steam. The supplementary water supplied to the steam compressor (S-CP) is preferably pure water, in which ions and oxygen are removed, and may be input into the process by adding saturated steam while reducing the superheat of the steam. The flow rate of the supplementary water may be 0.1 ton / hour to 30 ton / hour or 1 ton / hour to 20 ton / hour, but is not limited thereto.

[0088] The high pressure steam flowing out of the steam compressor (S-CP) may finally have a temperature of 140°C to 280°C or 150°C to 240°C.

[0089] As described above, according to the present invention, a plurality of waste heat sources are each heat-exchanged with cooling water, and each heated cooling water is introduced into the heat pump device through an integrated pipe to heat-exchange with the refrigerant flow circulating in the heat pump device, thereby recovering the waste heat of the heated cooling water. The waste heat of the cooling water is used to evaporate the refrigerant, which is compressed using electricity and exchanges heat with water, thereby obtaining a large amount of steam or hot water required in the process. For example, the final amount of steam prepared according to the present invention can be 1 ton / hour to 120 tons / hour or 6 tons / hour to 100 tons / hour.

[0090] The heat of steam generation according to the present invention may be defined by the following Formula 1, and the coefficient of performance COP of the system applied to the method for preparing steam or hot water of the present invention may be represented by the following Formula 2.

[0091] [Formula 1]

[0092] Heat of steam generation = waste heat + supply power (power used for refrigerant compression and steam compression)

[0093] [Formula 2]

[0094] COP = heat of steam generation / supply power

[0095] The coefficient of performance (COP) according to the above formula 2 is defined as the ratio of the heat of steam generation (heat absorbed by water) to the electric energy input to the refrigerant compressor and the steam compressor. For example, when the COP value is 1.5, it means that the heat value obtained is 1.5 times the input electric energy.

[0096] The steam prepared according to the method of the present invention satisfies a COP value calculated by Formula 2 of 1.3 or more, in particular, 1.5 or more, thereby ensuring economic efficiency compared with input electrical energy.

[0097] According to the present invention, steam prepared in large quantities by connecting a plurality of waste heat sources to one heat pump device for waste heat recovery can be stored and distributed throughout the process and supplied to local user sources.

[0098] Hereinafter, the present invention will be described in more detail by examples. However, the following examples are used to illustrate the present invention, and it is clear to those skilled in the art that various changes and modifications may be made within the scope and spirit of the present invention, and the scope of the present invention is not limited thereto.

[0099] Embodiment 1:

[0100] like Figure 3 As shown, a system is used to recover waste heat and prepare steam / hot water, wherein the system includes three waste heat sources 100 , three heat exchangers 200 , and a single heat pump device 300 connected to the heat exchangers through an integrated pipe 10 .

[0101] (Step 1)

[0102] First, gaseous (75°C and 5 bar) process waste heat fluids WH1, WH2 and WH3 are each supplied to three waste heat sources 100 at a flow rate of 52 tons / hour, and heat exchange is performed by introducing a plurality of process waste heat fluids into each heat exchanger HE1, HE2 and HE3, in which cooling water at 30°C circulates at a pressure of 5 bar. After the heat exchange, the process waste heat fluids WH1, WH2 and WH3 in each heat exchanger HE1, HE2 and HE3 discharge heat and flow out in a liquid state at 65°C and 4 bar, and cooling water (40°C and 5 bar) heated by absorbing heat flows out.

[0103] (Step 2)

[0104] The flows of cooling water (40° C. and 5 bar) heated in the three heat exchangers HE1 , HE2 , and HE3 are merged in the integrated pipe 10 (straight length 50 m and flow velocity 1 m / s) and then supplied to the refrigerant evaporator (EV) of the heat pump device 300 .

[0105] The heat pump device 300 includes a refrigerant evaporator (EV), a refrigerant compressor (CP), a refrigerant condenser (CD) and a refrigerant expansion valve EP valve, and in the refrigerant evaporator (EV), a refrigerant (trans-1-chloro-3,3-trifluoropropene, R1233zd (E)) in a liquid state (25°C and 1.3 bar) circulates at a flow rate of 310 tons / hour and performs heat exchange with a mixed flow (40°C) of heated cooling water supplied through the integrated pipe 10.

[0106] After heat exchange, the mixed flow of cooling water in the refrigerant evaporator (EV) is cooled to 30°C and then circulated to each heat exchanger HE1, HE2 and HE3 through multiple branch pipes connected to pipe 20, and the refrigerant is vaporized by absorbing heat and flows out in a gaseous state at 25°C and 1.3 bar.

[0107] (Step 3)

[0108] After the gaseous refrigerant stream was introduced into the refrigerant compressor (CP), compression was performed at a power of 9.9 Gcal / h to obtain a gaseous compressed refrigerant stream at 128° C. and 16 bar.

[0109] (Step 4)

[0110] A compressed refrigerant stream (128° C. and 16 bar) is introduced into a refrigerant condenser (CD), and water (20° C. and 5 bar) is supplied to the refrigerant condenser (CD) at a flow rate of 38 tons / hour for heat exchange. In this case, for a pipe through which water is supplied to pass through the refrigerant condenser (CD), the outlet pressure of the pipe, i.e., the discharge pressure of the water is adjusted to 2 bar using a pressure control valve provided on the pipe so that the output pressure of the pipe is maintained less than the vapor pressure (2.3 bar) at the temperature of the heat-exchanged water (124° C.). In this way, 38 tons / hour of heat-exchanged water at 124° C. and 2 bar is obtained in the form of steam, and the refrigerant stream is condensed and flows out as a liquid at 120° C. and 16 bar.

[0111] (Step 5)

[0112] The condensed refrigerant stream (120° C. and 16 bar) passes through an expansion valve (EP valve) to obtain a liquid refrigerant stream of 25° C. and 1.3 bar, and then circulates to a refrigerant evaporator (EV).

[0113] Embodiment 2:

[0114] The procedure of Example 1 is carried out, except that in step 4, water (20°C and 5 bar) is supplied to the refrigerant condenser (CD) at a flow rate of 240 tons / hour, and the outlet pressure of the supply water pipe is adjusted to 2.5 bar so that at the temperature of the heat-exchanged water (124°C), the outlet pressure is maintained above the vapor pressure (2.3 bar), thereby obtaining 240 tons / hour of hot water at 124°C and 2.5 bar by the heat exchange between the compressed refrigerant and water (20°C and 1 bar).

[0115] Embodiment 3:

[0116] The procedure of Example 1 was carried out except that the vapor obtained in the refrigerant condenser (CD) was transferred to the vapor compressor (S-CP) for additional compression.

[0117] By supplying water (20°C and 5 bar) at a flow rate of 38 tons / hour at a power of 4.0 Gcal / h for compression, steam at 200°C and 13 bar is finally produced at a rate of 45 tons / hour. When additional water is supplied to cool the superheated steam in the steam compressor, the amount of steam finally produced increases compared to the amount of water initially supplied.

[0118] For the finally prepared steam, the heat of steam generation was calculated according to the following Formula 1, and the coefficient of performance (COP) was calculated according to the following Formula 2.

[0119] [Formula 1]

[0120] Heat of steam (or hot water) generation = waste heat + supply power (power used for refrigerant compression and steam compression)

[0121] [Formula 2]

[0122] COP = heat generated by steam (or hot water) / power supplied

[0123] Embodiment 4:

[0124] The procedure of Example 1 is carried out, except that the gaseous refrigerant stream is compressed in the refrigerant compressor (CP) at a power of 6.9 Gcal / h to obtain a refrigerant stream compressed to a gaseous state at 98°C and 7.8 bar, and then the compressed refrigerant stream is heat exchanged with 27 tons / hour of water (20°C and 1 bar) in the refrigerant condenser (CD) to prepare steam at 78°C and 0.4 bar, and the condensed refrigerant stream at 87°C and 7.8 bar flows out and is transferred to the expansion valve (EP valve).

[0125] The steam obtained in the refrigerant condenser (CD) is compressed by transferring it to a steam compressor (S-CP) and supplying water (20°C and 1 bar) at a flow rate of 30 tons / hour at a power of 3.5 Gcal / h, thus finally preparing steam at 149°C and 3.9 bar in an amount of 35 tons / hour.

[0126] Embodiment 5:

[0127] The procedure of Example 1 is carried out, except that the flow rate of the integrated pipe is changed to 0.3 m / s, and the steam obtained in the refrigerant condenser (CD) is transferred to the steam compressor (S-CP) for additional compression by supplying water (20°C and 5 bar) at a flow rate of 38 tons / hour at a power of 4.0 Gcal / h.

[0128] Embodiment 6:

[0129] The procedure of Example 1 is carried out, except that the flow rate of the integrated pipe is changed to 6 m / s, and the steam obtained in the refrigerant condenser (CD) is transferred to the steam compressor (S-CP) for additional compression by supplying water (20°C and 5 bar) at a flow rate of 38 tons / hour at a power of 4.0 Gcal / h.

[0130] Comparative Example 1:

[0131] like Figure 5In the process shown, three heat sources 100 containing process waste heat fluids WH1, WH2 and WH3 are respectively supplied to heat exchangers HE1, HE2 and HE3 to exchange heat with cooling water under the same conditions as in Example 1, and then the mixed flow of heated cooling water (40°C and 5 bar) flowing out of each heat exchanger is supplied to a cooling tower (CT) and cooled.

[0132] Specifically, the cooling tower is an open forced air countercurrent type commonly used in the art, and a mixed flow of heated cooling water is supplied to the filler through a nozzle installed at the upper portion of the cooling tower, and the air introduced by the upper fan of the cooling tower contacts the cooling water on the filler in a countercurrent contact manner, and is thus dissipated into the atmosphere while maintaining moisture equal to the amount of saturated steam. In this process, the cooling water is reduced in temperature by evaporation latent heat, and is collected in a lower water tank, and then circulated to each of the heat exchangers HE1, HE2, and HE3.

[0133] In other words, the mixed flow of cooling water heated in the cooling tower cannot be recovered since the heat is forcibly dissipated by contact with the air.

[0134] The results of recovering waste heat from heated cooling water in the above-mentioned Examples and Comparative Examples are shown in Table 1 below.

[0135] [Table 1]

[0136]

[0137] As can be seen from Table 1, in Comparative Example 1, since the heat is forcibly dissipated by contact with the air in the cooling tower (CT), it is impossible to recover the cooling water heated by heat exchange with a plurality of waste heat sources. On the other hand, in Examples 1 to 6, a plurality of waste heat sources are each heat exchanged with cooling water, and then the heated cooling water is introduced into the heat pump device through an integrated pipe, and the waste heat of the heated cooling water can be recovered by heat exchange with the refrigerant flow circulating in the heat pump device, and steam or hot water can be prepared using the recovered waste heat.

[0138] Specifically, Example 3 satisfies the flow rate of the integrated pipe in the range of 0.5m / s to 5m / s to maintain uniform mixing of the heated cooling water flow, and controls the temperature of the refrigerant condensed in the refrigerant compressor to above 85°C to maintain the temperature of the steam obtained in the refrigerant condenser to above 85°C, and then performs additional steam compression, so the difference between the initial waste heat temperature and the final prepared steam temperature, that is, the temperature increase is the highest.

[0139] Meanwhile, Example 4 satisfies the flow rate of the integrated pipe in the range of greater than 0.5 m / s to 5 m / s, but as the temperature of the compressed condensed refrigerant is as low as 75° C., the obtained steam is as low as 78° C., so the temperature increase is insufficient even after the steam is compressed. In addition, due to air leakage caused by the low pressure of the steam, the steam is contaminated, resulting in corrosion and erosion of the pipe, and as a result, the temperature and pressure of the steam finally prepared are lowered compared to Example 3.

[0140] In the case of Example 5, as the flow rate of the integrated pipe is as low as 0.3 m / s, the heat mixing efficiency of the refrigerant vaporized at the front end of the refrigerant compressor is reduced, resulting in large changes in the temperature and pressure of the refrigerant. As a result, surge and cavitation phenomena occur in the refrigerant compressor and the steam compressor, and the amount of steam changes at the rear end of the steam compressor, resulting in pressure changes. As a result, the temperature, pressure and coefficient of performance (COP) of the steam finally prepared are reduced compared with Example 3.

[0141] In the case of Example 6, as the flow rate of the integrated pipe was as high as 6 m / s, erosion and vibration occurred in the refrigerant pipe at the front end of the refrigerant compressor. As a result, since it was difficult to operate the refrigerant pipe for a long time, maintenance or pipe replacement was required, and the eroded foreign matter caused damage to the rotating components in the compressor due to vibration and caused noise. As a result, the temperature, pressure and coefficient of performance (COP) of the steam finally prepared were reduced compared with Example 3.

[0142] Explanation of symbols

[0143] 100: Multiple waste heat sources including process waste heat fluids (WH1, WH2, WH3, ...)

[0144] 200: Multiple heat exchangers (HE1, HE2, HE3, ...)

[0145] 300: Heat pump device

[0146] EV: Refrigerant Evaporator

[0147] CP: Refrigerant compressor

[0148] CD: Refrigerant condenser

[0149] EP valve: refrigerant expansion valve

[0150] 10, 20: Integrated pipe:

[0151] S-CP: Steam Compressor

Claims

1. A method for preparing steam or hot water, comprising the following steps: (S1) introducing a process waste heat fluid supplied from a plurality of waste heat sources into each of a plurality of heat exchangers configured in a number corresponding to the plurality of waste heat sources to exchange heat with cooling water; (S2) introducing the cooling water heated by heat exchange with the process waste heat fluid in each heat exchanger into the refrigerant evaporator via an integrated pipe, and then exchanging heat with the refrigerant to evaporate the refrigerant; (S3) compressing the evaporated refrigerant flow in a refrigerant compressor; (S4) exchanging heat between the compressed refrigerant stream and water in the refrigerant condenser, thereby condensing the refrigerant stream and obtaining steam or hot water; and (S5) The condensed refrigerant flow is passed through a refrigerant expansion valve for decompression and then circulated into the refrigerant evaporator.

2. The method according to claim 1, wherein: The heated cooling water is cooled by the heat exchange in the refrigerant evaporator, and then branched out and then circulated to each of the plurality of heat exchangers used in step (S1).

3. The method according to claim 1, wherein: In step (S1), the temperature of cooling water introduced into each of the plurality of heat exchangers is 10°C to 50°C, and the cooling water is heated to a temperature of 13°C to 60°C through heat exchange.

4. The method according to claim 1, wherein: The linear length of the integrated pipe is 5 m to 5000 m and is controlled to maintain a flow velocity of 0.5 m / s to 5 m / s.

5. The method according to claim 1, wherein: The refrigerant introduced into the refrigerant evaporator has a pressure of 0.5 bar to 40 bar and a temperature of 10°C to 60°C.

6. The method according to claim 1, wherein: The refrigerant compressor uses electrical energy to increase the pressure of the refrigerant flow introduced into the refrigerant compressor by 1.2 to 5 times.

7. The method according to claim 1, wherein: The temperature of the compressed refrigerant stream is from 90°C to 200°C.

8. The method according to claim 1, wherein: The temperature of the refrigerant stream condensed by the heat exchange with water in the refrigerant condenser is 85°C to 170°C.

9. The method according to claim 1, wherein: The temperature of the hot water obtained by heat exchange between the refrigerant flow and water in the refrigerant condenser is 85°C to 180°C.

10. The method according to claim 1, wherein: The hot water is obtained by adjusting the water passing through the refrigerant condenser to be discharged at a pressure higher than its vapor pressure.

11. The method according to claim 1, wherein: The pressure of the steam obtained by heat exchange between the refrigerant flow and water in the refrigerant condenser is 0.5 bar to 16 bar.

12. The method according to claim 1, wherein: The steam is obtained by conditioning the water passing through the refrigerant condenser to exit at a pressure below its vapor pressure.

13. The method according to claim 1, wherein: The vapor exiting the refrigerant condenser is further compressed, converted to high pressure vapor, and then used as a process heat source.

14. A system for preparing steam or hot water, comprising: a plurality of waste heat sources, a plurality of heat exchangers arranged in a number corresponding to the plurality of waste heat sources, and a heat pump device connected to the plurality of heat exchangers through an integrated pipe and branch pipes, The heat pump device comprises a refrigerant evaporator, a refrigerant compressor, a refrigerant condenser and a refrigerant expansion valve connected by pipes. The heated cooling water flowing out of each of the plurality of heat exchangers is collected through an integrated pipe and introduced into the refrigerant evaporator of the heat pump device, then exchanges heat with the refrigerant to evaporate the refrigerant, passes through branch pipes, and then circulates to each heat exchanger.

15. The system of claim 14, wherein: The refrigerant condenser of the heat pump device is connected to a further vapour compressor.

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